Process of electrolytic decomposition of chlorides



- E.;S CHLUMBERGER PROCESS OF ELECTROLYTIC DECOMPOSITION'EF CHLORIDESFiledwspt. 17, 1925 Hydrogen t Fig.2

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tame ERNST SCHLUMBERGER, 0F BERLIN-LICHTERFELDE-OST, GERMANY, ASSIGNOROF THREE-FOURTHS TO THE FIRM KOHOLYT AKTIENGESELLSCHAFT, OF BERLIN,

GERMANY.

PROCESS OF ELECTROLYTIC DECOMIOSITION OF CHLORIDES.

Application filed September 17, 1925. Serial No. 56.941. and in GermanyJuly 28. 1924.

This invention relates to improvements in the productlon of alkali andchlorine hy electrolytic decomposition of alkali metal chloridesolutions. In this process, anodes made of carbon or plui'nbago aregenerally used, but such anodes are subject to a conslderabledrawback,inasmuch as they are more or less attacked by the electrolyticvaction and must I be renewed after a relatively short time. It has beenknown for a long time that this attack is attributable to the porosityof theelectrodes, and therefore it has been pro posed to do away withthe porosity of the electrodesby impregnating them with tar, paraflin,linseed-oil or the like.

New I have found that the attack of the carbon or plulnbago electrodesmay be redueed to a considerable extent without any impregnation, ifcare be taken that the pores of the electrodes are permanently kepttilled with fresh salt solution. This end may be attained by conductingthe salt solution into the electrolytic cell wholly or partially throughthe pores of the electrode. As everybody knows, the different electrodesmanufactured for electrolytic purposes by baking, possess a smaller orgreaterdegree of porosity due to this baking process; I have found that.this porosity sutlices to pass through the pores the whole of the saltsolution required. The solution may be passed through flat electrodesfrom one side to the other; but the best method of introducingthesolution is to provide'the carbon anodes with suitable borings or hollowspaces through which the electrolyte is introduced.

For the purpose of uniform distribution the said borings or hollowspaces are formed in such a manner that nearly equally sized ways aretraversed by the solution in the interior of the electrode.

I am aware that a process for decomposing salts by'electrolysis has beenproposed, in which filter electrodes are employed, but in this .case theelectrodes used act simultaneously as electric conductors and as afiltering device and their purpose is to separate the ions formed fromthe electrolyte after the electrolysis has been effected, that is tosaythey act like a porous diaphragm. However, according to this knownmethod the electrolyte is introduced into the bath in the ordinary Way,that is to say'by letting it simply flow in. In contradistinction tothis, according to my improvedprocess electrolysis takes place afterfiltration. Strictly speaking-there is no question of filtration at all,as the porous electrode only serves to introduce the undecoinposedelectrolyte into the bath proper, without the necessity of separatingthe ditterent components. Only after the passage does electrolysis take'place. Thus the two processes dill'er in principle.

In the accompanying drawing I have .illustrated two types ofelectrolytic cells provided with anodes embodying my invention; Fig. 1is avertical cross-section through an electrolyser of the Nelson type.Fig. 2 is a vertical longitudinalsection through a cell of thewell-known llilliter type. and Fig. 3 is a plan View of the anode ofthis cell.-

In Fig. 1 a is the outer wall of the electrolytic cell which is dividedby a porous diasphragn'i I) into the anode chamber cand the cathodechamber (Z. a is the cathode formed of perforated sheet iron and f-is agraphite or pluinbago bar prepared according to my invention and formingone of the anodes. It is provided with a longitudinal central boring 9closed at its lower end and communicating by a flexible connectionh'with a funnel 2'. The electrolyte is introduced through pipe 70 and,if required, an addi tional quantity of electrolyte may be suppliedthrough pipe Z. The chlorine gas developed atthe anode escapes throughpipe m, The alkali solution is drawn off by pipe '22, and the hydrogengas is carried off by p ne.

During the constant course of the electrolytic process the quantity ofsalt solution supplied by pipe Z: tot-he interior of the graphite anodeis made equal to the quantity of electrolyte which is desired to passthrough the porous diaphragm. This quantity is regulated either bycontrolling the hydrostatic pressure in the interior of the anode, i. e.by suitable adiusting the level of the: salt solution in the funnel z orby correspondingly dimensioning the width of the boring 9. As understationary conditions the streaming velocity of the electrolyte remainspractically constant. both the hydrostatic pressure and the width of theboring {I can easily be determined by a preliminary trial.

The durability of the electrode is considerably increased, asshown'bythe following Two cells of the same construction were connectedin series so that the intensity of the electric current was the same inboth cells. The anode in both cells was formed of cylindrical graphitebars provided with a central boring. The weight of the anode of thefirst cell was 51.7 grams before the trial.

However the electrolyte was not passed through the boring of the anodebut was directly introduced into the anode chamber.

tours also of both electrodes presented a dif ferent appearance. Thesecond eectrode which had been traversed by the electrolyte, hadpreserved its original dlmensions, especially the corners at its lowerend had retained their sharpness, whereas the other electrode showeddistinct wear and tear and especially the corners were rounded off.

Figs. 2 and 3 illustrate in diagrammatic longitudinal section and inplan view a cell of the Biliiter-type. The cell 19 is divided by aporous diaphragm '9 into alower,

' cathodic chamber 11 and an upper, anodic chamber tfis the cathode madeof perforated sheet iron or netting work, and uis the graphite anodeconstructed and ar;

ranged according to my present invention.

The anode plate is provided with a num'ber ofparallel longitudinalborings o,-the ends -of which are closed by exactly fittingplugs 'w. Theplate is supported .by a graphite bar :12 provided. with a longitudinalcentral boring 7 which however does not wholly penetrate the bar. Theend of the harm is screw-threaded, so that it may be screwed into acorresponding opening in the anode plate, which is provided with acorresponding female screw-thread. As an alternative, the end of the barmay be tapered by grinding off and may be driven into a correspond- The'elecing-conical boring of the anode plate. In any case the end of thebar a; is provided with radial borings .2 which are made to comthecarbon anodes are not absolutely protected against attack by passing thesalt solution through the pores of the anodes in the direction of thepositive electric current. The attack was only diminished to about onethird. On I further investigation I have found that. the attack of theelectrodes can further be diminished to a considerable extent byacidifying the electrolyte introduced into the bath, preferably by theaddition of a suitable acid. In some cases, the acid, preferable dilutedhydrochloric acid, may be passed alone through the pores of the anode,whereas the neutral electrolyte itself is introduced into a cell in theordinary way. As the attack of the anodes is probably due to theoxidizing action of the immigrating OH-ions, according to my presentprocess a sufficiently acidity is always maintained in the anode poresto neutralize immediate'y the arriving OH-ions, so that they cannotinjurethe electrode by anodic discharge.

I claim 1. In the process of electrolytic decomposition of chlorides bymeans of carbon or graphite anodes the method of introducing anelectrolyte into the bath through the pores of the said anodes.

2. Process in accordance with claim 1, in which "the electrolyte isintroduced through hollow'spaces or borin s suitable arranged I in theinterior of the anodes.

3. Process in accordance with claim- 1, in which the electrolyteisintroduced through hollow spaces or boring's arranged in the in teriorof the anodes in such amanner that the distances traversed by theelectrolyte in the interior of the anodes are approximately equal inlength. r

4. Process inaccordance with claim 1, in which an acid electrolyte isintroduced through the pores of the anode.

In testimony whereof I aflix my signature.

ERNST SCHLUMBERGER.

